Python Inner Working

What is python?

Python is like a bridge between human thinking and computer logic. It’s a language that doesn’t try to complicate things — instead, it lets you express ideas in code almost as naturally as you think them.

It feels more like writing instructions to a smart friend than programming a machine. You don’t have to worry much about complex syntax or structure — you focus on what you want to build.

Whether it’s analyzing huge datasets, building websites, or training AI

Professionally speaking, Python is:

• Dynamically typed – you don’t need to declare variable types.

• Interpreted – it runs line by line through an interpreter.

• Multi-paradigm – supports object-oriented, procedural, and functional programming styles.

• Extremely flexible – widely used in automation, data science, machine learning, web development, scripting, software testing, and more.

🔍 Inside Python: What Really Happens Behind the Scenes?

Have you ever wondered how Python understands your code? You write simple lines like print("Hello, world!"), but under the hood, Python is doing a lot of heavy lifting — from compiling to bytecode to memory management and more.
In this blog, we’ll take a beginner-friendly peek into the engine room of Python. No complex jargon, just a clear and curious exploration of how your favorite language really works.

How Python Runs Your Code: Step-by-Step

Have you ever wondered what happens behind the scenes when you run a Python program? Let’s break down the journey of a simple script, for example:

print("Hello, world!")

From the moment you write the code to when “Hello, world!” appears on your screen, Python goes through several stages. We’ll walk through each stage in clear terms.

1.✍️Code Editor

First, you write your code in a code editor or IDE (like VS Code, PyCharm, Jupyter Notebook or even a simple text editor). The editor is just a tool where you type your Python commands. In our example, the editor window contains:

print("Hello, world!")

This is the human-readable code you wrote. At this point, nothing is happening yet to run the code – the code just lives in the editor. When you save the file, you choose a filename with a .py extension (for example, hello.py). This saved file is where your code is stored for Python to use.

2. 📄Source File (.py)

When you save your code, it becomes a Python source file (for example, hello.py). This file contains the exact text you wrote – in this case, the line print("hello python"). The source file is just plain text on your disk. Computers can’t execute this text directly because they only understand machine code (binary instructions)

Instead, Python reads this file as input. The source file is like a recipe written in English – it tells the computer what to do, but it’s not in the computer’s native language yet. For instance, our hello.py file has one line of code that tells Python to print a greeting.

3. 🧰Compiler

Next, when you run the Python program (for example by typing python hello.py in a terminal) or directly click the run button in VS Code, the Python interpreter takes over. Python is often called an interpreted language, but under the hood, it does a compilation step first. The interpreter (such as CPython) takes your .py source file and compiles it into bytecode.

This means Python checks your code for errors and transforms it into a lower-level form. In our example, print("hello python") is converted into Python Bytecode. At the same time, Python may create a compiled file named something like hello.cpython-311.pyc inside a __pycache__ folder (the number matches your Python version). This .pyc file stores the bytecode so Python can run your code faster next time.

In simple terms, the compiler in python translates your readable code into bytecode- an intermediate form that the Python Virtual Machine (PVM) can understand.

4. 📦Bytecode

Bytecode is the result of the compilation step. It’s a set of instructions, but not quite machine code. Think of bytecode as Python’s own low-level language. It’s still not directly understandable by the CPU, but it’s much closer to what the computer can execute compared to your original text. Bytecode is platform-independent, which means the same bytecode can run on any operating system that has the same Python interpreter.

For our print("hello python") example, Python might generate bytecode instructions like load the string “hello python” and “call the print function”. You don’t usually see this bytecode, but it’s saved in a .pyc file inside a __pycache__ folder. The __pycache__ folder is Python’s way of caching compiled bytecode files. On later runs, Python will use this cached bytecode (if the source hasn’t changed) to start your program more quickly.

In summary, bytecode is an intermediate, “almost machine” code that Python will execute. It’s saved in .pyc files in a special folder (__pycache__).

e.g.: I create a file named test_hello.py. Here you can see I imported the hello.py file to test_hello.py file then I hit run button after that a __pycache__ folder created.

💡 For example, importing a file named helper.py will generate a compiled file like hello.cpython-313.pyc.

🗂️ Why __pycache__?

Python uses the __pycache__ folder to keep things organized and clean. If every .pyc file were saved in the main directory, your project folder would quickly become messy — especially in larger applications with dozens of modules.

5. 🖥️Python Virtual Machine

Once the bytecode is ready, it’s time for the real work to happen — and that’s where the Python Virtual Machine (PVM) comes in.

The PVM is a software-based engine that gets installed automatically when you install Python. You don’t need to install it separately — it’s already bundled in your Python distribution. You can think of it as an engine that executes the bytecode instructions one by one. The PVM loads the bytecode (from the .pyc file or directly from memory) and then enters a loop: it reads each bytecode instruction, decodes it, and performs the corresponding action.

🔁 The Loop That Runs Your Code:

Inside the PVM, there’s a loop running continuously. This loop is the heart of the interpreter. When you push a .pyc bytecode file into it (via imports or running Python code), the PVM starts executing the bytecode instructions line by line.

That’s exactly why Python is known as an interpreted language — because this loop acts like an interpreter that runs your code step-by-step, not all at once like in compiled languages.

The PVM is also referred to as Python’s runtime engine — a necessary software component without which the code simply won’t run. Every programming language has its own runtime:

• Java has the JVM (Java Virtual Machine)

• JavaScript has V8 Engine

• Python has the PVM

Without this runtime engine, even compiled bytecode (.pyc) would just sit there — doing nothing. The PVM is the one that takes action and produces the output you see.

So in short:
🧠 PVM is the brain behind Python execution. It reads bytecode, runs a loop internally, and line-by-line brings your code to life.

6. 🚀Running Program

Finally, after the PVM executes the instructions, you see the result. In our example, the bytecode was telling Python to print text to the screen. The PVM runs the print function, which sends "Hello, world!" to the standard output (your console or terminal). The user (you) then sees: appear on the screen. This is the running program’s output.

🎯 Conclusion: Python Does the Heavy Lifting for You

You write simple code like print("hello python") — but behind the scenes, Python sets an entire system in motion. From compiling your code to bytecode, organizing it smartly in __pycache__, and finally running it through the powerful Python Virtual Machine — Python handles all the complex stuff so you don’t have to.

That’s the beauty of Python:
👉 It’s simple on the surface, but powerful underneath.
All you need to do is write — Python takes care of the rest.